1. Field of the Invention
The present invention relates to a zoom lens and more particularly to a compact zoom lens having a high variation factor which is suitable to a still camera and a video camera.
2. Related Background Art
A compact zoom lens having a relatively high variation factor for use in a still camera or a video camera is proposed in Japanese Laid-Open Patent Application No. 56-1009. The disclosed zoom lens comprises a first lens group having a positive refractive power, a second lens group having a negative refractive power, an iris and a third lens group having a positive refractive power, arranged in this sequence as viewed from an object. The first lens group, the iris and the third lens group are reciprocally moved convexly to the object and the second lens group is monotonously moved from an object end to an image end when the lens is zoomed from a wide end to a telephoto end. In this manner, a compact zoom lens having a high variation factor is attained.
In order to attain a compact zoom lens having a high zoom ratio, refractive powers of movable lenses are increased and intervals between lenses are shortened as a usual method.
In the zoom lens described above, the compactness is attained by the above construction, the loci of movement and the narrow interval between the second lens group and the third lens group.
However, since a principal point of the third lens group facing the object is relatively close to the image plane, there is a limitation in narrowing the interval between the second lens group and the third lens group in order to reduce the size.